Aryl acetonitriles are produced by reaction of cyanogen chloride and aromatic or heteroaromatic methylene or methyl compounds which contain an active hydrogen at a temperature of 500.degree. C. up to 1200.degree. C., Grimm, Menting, Ind. Eng. Chem. Prod. Res. Div. Vol. 14 (1975), No. 3, pages 158-161 as well as Dixon U.S. Pat. No. 2,553,404 and Dixon U.S. Pat. No. 2,606,917.
Further compounds which can be produced by reaction of cyanogen chloride and corresponding methyl or methylene compounds are proposed in German OS No. 2854210 and related Schalke U.S. application Ser. No. 102,933 filed Dec. 12, 1979, abandoned.
The entire disclosures of Grimm, U.S. Pat. Nos. 2,553,404 and 2,606,917 and German OS No. 2854210 and related Schalke U.S. application Ser. No. 102,933 are hereby incorporated by reference and relied upon. More especially, the present invention can be employed to prepare aromatic or heteroaromatic nitriles from any of the aromatic or heteroaromatic methylene or methyl compounds mentioned in the disclosures relied upon.
In the production of nitriles according to the process referred to above there is the difficulty of isolating the product from the hot reactor gases in a simple way and avoiding loss of the product and excess or unreacted starting materials. There must be a quick separation or neutralization of the hydrochloric acid formed.
In the article of Grimm and Menting (Loc. cit.) which besides the production of phenylacetonitrile also is concerned with phenylmalonodinitrile there is described two different methods for the isolation of phenylacetonitrile from the reaction mixture.
The precipitation of the fine gas mist formed in the condensation with simply cooling using a reflux condenser, see Grimm and Menting (loc. cit.), is only very incomplete. The reason is that with this method the hydrochloric acid cannot be neutralized and as a result there can be caused decomposition of the product and starting material.
Thereby the direct distillation of the reaction gas mixture formed with phenylacetonitrile does not lead to a color stable product. Also the conversion of this nitrile into a color stable acetate could only be carried out with technical difficulties.
Likewise there occur difficulties in collecting the reaction gases in a methanol bath since a part of the nitrile is changed into the corresponding ester.
In Dixon U.S. Pat. No. 2,553,404 and Dixon U.S. Pat. No. 2,606,917, in principle there is condensation in the same way. In U.S. Pat. No. 2,606,917 there is formed in the reactor with the jointly fed steam in the condensation a concentrated hydrochloric acid which attacks the product and partially saponifies it.
For these reasons the yields stated in these patents are clearly lower than in the other known processes.
Water or water containing cooling agents are also employed as a direct condensation agent, see German OS No. 2854210 and Schalke U.S. application Ser. No. 102,933. The aqueous hydrochloric acid formed thereby, however, can be strongly corrosive to the apparatus and also can act saponifyingly on the product formed. For this reason the reaction gas mixture should then be simultaneously neutralized during the cooling according to this proposal.
In German OS No. 2854210 and related Schalke U.S. application Ser. No. 102,933, it is recommended that the gas mixture leaving the reactor be cooled or quenched to a temperature below 100.degree. C. and therewith the gas condensed. It should also be favorable according to this for the purpose of quicker cooling to inject into the gases a cooling agent, preferably water. In this case, the water can contain basically acting materials such as alkali hydroxide, alkali carbonate or alkali bicargonate, for the neutralization of the hydrochloric acid formed in the reaction. However, difficulties occur hereby through the waste water formed which still contains highly toxic materials, as e.g. starting material dissolved in water, product, unreacted cyanogen chloride, byproducts and decomposition products of the reaction. These toxic materials are difficult to eliminate.
The cooling agent is generally injected into the reaction gas. For better distribution therein and quicker cooling of the reaction gas there additionally is the danger of clogging of a nozzle by the carbon black particles present in the condensed product or by solid neutralization products. The chloride containing solution, formed at the point of injection at elevated temperature in the use of water or water containing cooling agent, can also lead to corrosion problems. These cannot be overcome or can only be overcome with difficulty with the metallic work materials needed at this place.
Furthermore very disadvantageous in the industrial recovery of the nitrile is the fact that the nitriles which are sensitive to hydrochloric acid in the previously customary distillative working up of the crude reaction mixture are present over long periods of time with the hydrochloric acid or hydrogen chloride formed.
Only after distillation of the reactants employed in addition to cyanogen chloride, which reactants are employed in two or threefold excess is the distillation of the nitrile formed begun. In the meantime, however, the nitrile itself already is attacked to a considerable degree. Additionally, the respective reactant with cyanogen chloride generally is more thermally stable than the nitrile formed from it.
Thus in this method of operation both the yield as well as the purity of the isolated product and also the recovery of the starting material are hurt; besides there is formed a higher portion at the distillation sump.
The known methods of condensation thus lead to losses of material or to industrial difficulties in the recovery of the nitrile concerned from the reaction gas mixture.